Sky Data

Civil twilight is a period when the sun’s disk is less than six degrees of arc from the horizon. It precedes sunrise and follows sunset by about one half hour. During these times, it is usually possible to read outdoors without the benefit of artificial light. However, only the brightest celestial objects may be visible during civil twilight.

Sunrise is at 7:18 a.m. Sunday January 15, and sunset occurs at 4:52.

On the last day of the month Tuesday January 31, sunrise is at 7:07 with sunset at 5:11 p.m. The sun is then located in Capricornus. During January, the length of time the sun is above the horizon each day increases by 45 minutes.

In January average overnight temperatures recorded near Belvedere Castle in Central Park drop slightly from 27 degrees Fahrenheit on the first of the month, to 26 degrees on the 31st. On that day the sun is in the constellation Capricornus.

Principal Phases of the Moon this month are:

First Quarter

January 1

Full Moon

January 9

Last Quarter

January 16

New Moon

January 23

First Quarter

January 30

This month there will be two occasions when the moon is at its first quarter phase. Perhaps the lunar event on January 30 might then be called a “Blue First Quarter Moon”. (See last month’s Sky Reporter for a reminder why first and last quarter lunar phases look like “Half Moons” when seen in the sky.)

On Wednesday January 4, at 8 p.m., the Earth reaches perihelion, when we are at the year’s minimum distance from the sun, about 91,376,000 miles.

Sky Cast

At 6 a.m. the morning of New Year’s Day, Mars is quite bright at magnitude 0.2, near the meridian in the constellation Leo. Saturn has magnitude 0.7 in Virgo, and is high in the southeast. At that time, Mercury has just risen in Ophiuchus with magnitude minus 0.4.

At 5 p.m. the evening of January first, the first quarter moon is in Pisces, 13 degrees of arc to the upper right of Jupiter as you face southeast. Jupiter, at magnitude minus 2.6, clearly outshines bright stars of winter evenings such as Sirius and Rigel.

However during January even Jupiter yields visual primacy to Venus, currently brilliant above the southwest horizon at magnitude minus 4.0. On January first, Venus sets three hours and 17 minutes after the sun.

Monday January 2 the moon is just four degrees of arc from Jupiter. If you have never pointed out the solar system’s largest planet to a friend or relation, this is a perfect night to do so, if the sky is clear.

Monday the 9th, the Full Wolf Moon is located near twin stars Castor and Pollux in Gemini and the bright star Procyon in the constellation of the Little Dog, Canis Minor.

During early mornings of January 13 and 14 the waning gibbous moon is 10 degrees south of Mars. On Monday, the 16th, the Last Quarter moon is in Virgo, forming a small triangle with nearby Saturn and first magnitude star Spica.

During twilight and early evenings of Wednesday January 25 and Thursday the 26th the crescent moon might be seen part of a beautiful configuration with Venus in our southwestern sky. We may also notice that the apparent distance between Venus and Jupiter is diminishing week to week. In March both planets will form a magnificent pair that will be joined for several nights by that month’s crescent moon.

On Sunday and Monday January 29 and 30 the moon moves pass Jupiter, flanking the big planet at an apparent distance of about six degrees each night.

At the end of January Venus, with magnitude minus 4.1, sets at 8:31 p.m., three hours and 20 minutes after the sun.

The evening of January 31 Mars rises at 8:27 p.m. Saturn rises at 11:33 p.m. and Jupiter sets at midnight.

Sky Lore

Late last month NASA scientists announced the Kepler space observatory had discovered two Earth sized planets, designated Kepler 20e and Kepler 20f. Kepler is searching an area of sky near bright stars Deneb and Vega. Although we usually consider these objects typical features of summer skies, they remain visible above our northwest horizon for some time after twilight fades during January evenings.

On New Year's Eve, about six minutes before midnight, when the ball is almost ready to drop at Times Square, Sirius the brightest star in our night sky, reaches its highest altitude of the night as it crosses the celestial meridian. Clearly, gloves, hat, and warm clothing contribute to stargazing pleasures this month.

Aside from frosty temperatures, January is a good month to enjoy celestial views. An exceptional set of bright stars centered on the constellation Orion graces our evening sky. In addition, Venus now dominates in the southwestern direction for several hours after sunset.

Informal groupings of stars known as asterisms, including those forming the Belt of Orion, the Twins of Gemini, and the celestial Winter Oval are, during winter, viewed through atmosphere comparatively low in thermal energy. This air is less able to suspend dust and droplets of moisture more common in warmer months. This condition results in greater transparency and relatively darker skies through which we may better perceive stars.

Throughout evenings of January brilliant winter stars are on display across our southern sky. Around midnight, nearly directly overhead, we may see the star Capella, shining with magnitude zero. The great asterism known as the Winter Oval can be traced, starting with Capella and ranging clockwise to Aldebaran in Taurus, Rigel in Orion, Sirius in Canis Major, at magnitude -1.4 the brightest star in our night sky, then Procyon in Canis Minor, and finally to twin stars, Castor and Pollux of Gemini, pointing us back to Capella.